Binary chalcogenide glasses can be present in a number of optical systems, such as those employing infrared imaging. Although binary chalcogenide glasses can be desirable due to their wide transmission window in the infrared region of the electromagnetic spectrum, these glass materials can present a number of challenges that are not easily overcome. Many binary chalcogenide glasses exhibit significant variation in their refractive index as a function of temperature, and certain binary chalcogenide glasses have a coefficient of thermal expansion (CTE) that is mismatched with common metals used in the housings of optical systems, such as aluminum. Since many optical systems employing binary chalcogenide glasses are expected to operate over a wide temperature range, these shortcomings can result in significant performance issues. For example, thermal variation in the refractive index can result in image distortion if imaging is not conducted at the optimal temperature of a lens. Similarly, CTE mismatch can lead to mechanical failure at extreme operating temperatures if expansion rates are significantly different. In addition, many of the binary chalcogenide glasses that do exhibit desirable optical properties have poor thermo-mechanical robustness, such as unacceptable softness and low glass transition temperatures.
AMTIR-5 (Amorphous Materials, Inc.) is among the binary chalcogenide glass compositions described in U.S. Pat. No. 6,984,598. Although this binary chalcogenide glass exhibits low refractive index variability with temperature, it has poor mechanical properties and a relatively low glass transition temperature, both of which can be problematic for incorporating this glass material in various optical systems, especially those intended for deployment in extreme operating environments.
Ternary glass compositions are also commercially available. AMTIR-1 (Ge33As12Se55-Amorphous Materials, Inc.) and IRG 24 (Ge10As40Se50-Schott) are illustrative examples. However, the variation in refractive index with temperature remains rather high for these materials as well.
In view of the foregoing, optical materials having low refractive index variability as a function of temperature in combination with improved mechanical properties would be of considerable interest in the art. The present disclosure satisfies the foregoing need and provides related advantages as well.